Method of radio communication



May 27, 1941. P. H. DAVIS METHOD OF RADIO COMMUNICATION Filed June 6, 1938 TEE W M T Patented May 27, 1941 METHOD OF RADIO COIWMUNICATION Paul H. Davis, Chicago, Ill.

Application June 6, 1938, Serial No. 211,966

2 Claims.

My invention relates to high frequency radio transmitting and receiving apparatus, and more particularly to a novel method and means for transmitting intelligence.

It is a well-known fact that radio signals may be transmitted over greater distance for a given amount of power if the signal energy is concentrated in a uni-directional beam, than if the radiation field pattern of the signal energy has equal intensity in all horizontal directions. When the exact bearing of the receiving station is known or can readily be determined, uni-directional transmission of signal energy has proved highly satisfactory, and many different types of systems have been developed for this type of communication. If the bearing of the receiving station is not known, however, the usual form of beam transmitter cannot be employed, and a radiation pattern of substantially equal field intensity in all directions must be resorted to.

Now it is an object of the present invention to provide a high frequency radio communica tion system, which has many of the desirable characteristics of both systems in the transmission of signal energy over great distances and yet not necessitating a knowledge of the bearing of the receiving station.

More specifically, it is an object of this invention to employ a high frequency radio communication system in which the signal energy from the transmitter strikes the receiver intermittently, but at such a frequent interval that a persistence of sound effect is obtained in the receiver.

Another object of this invention is to provide a novel method and means for causing signal ener y to intermittently impinge on a receiver at a rate faster than the after image of sound.

A further object of this invention is to provide radio communication system in which a radio beam is rotated at a speed sufiicient to obtain a persistent after image of sound eifect at the receiving station located within the beam range but at an undetermined bearing position.

A still further object of this invention is to provide a novel radio communication system in which a radio beam is rotated at high speed until there is communication established with a movable receiving station, then rotated at a relatively slow speed until communication with the receiving station is again established, and finally maintaining the beam at a fixed bearing position.

Another and further object of this invention is to provide a novel method of radio communication.

Another and still further object of this invention, is to provide a novel high frequency antenna system which is economical to manufacture, is efficient in operation, and is rugged and reliable in use.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects 'and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic elevational view of a radio transmitter, receiver and antenna system embodying the features of the present invention; and

Figure 2 is a diagrammatic view illustrating the manner in which communication is established between a ground station and a station located on an aeroplane.

In Figure 1 of the drawing, high frequency radio apparatus is diagrammatically illustrated which is arranged to transmit a rapidly rotating beam of high frequency radio waves or signal energy. To this end, an antenna array is employed which includes a half-wave vertical antenna Ill, a reflector H and a director i2. Antenna Ill is connected through a coupling transformer I3 to a transmission line M leading to the transmitting and receiving apparatus 15 and I6 respectively, the transmitter and receiver being selectively connected to the transmission line M by a suitable relay ll.

Due to the relatively high end impedance of an end fed half-wave vertical antenna, and due to the relatively low surge impedance of the transmission line M, a quarter-wave impedance matching section I8 is inserted between antenna I0 and transmission line H. Impedance matching section 18 comprises two parallel conductors l9 and 20 which are connected together at their lower ends by the winding 2! of transformer l3. As is well known to those skilled in the art, an impedance matching section of this type is particularly well suited for connecting the transmission line to the antenna, since it has a very low impedance at its closed end and a relatively high impedance at its open end.

As is the common practice, conductor I!) of impedance matching section I 8 is formed continuous with thehalf-wave vertical antenna is,

and is preferably in the form of a single continuous rod or tube. It will be understood that the rod or tube which forms the antenna I and the conductor I9 is substantially three-quarters of a wave length long, while the conductor is substantially a quarter-wave length lon By locating reflector H and director l2 substantially a quarter-Wave length away from antenna l0 and on opposite sides thereof, a unidirectional pattern or beam of radio waves is obtained. As shown in the drawing, reflector l I and director l2 are mounted on a horizontally disposed arm 22, which is arranged for rotation about antenna 10. For this purpose, a supporting collar 23 is provided upon which a second collar 24, secured to the cross arm 22, is arranged to rotate, a suitable ball bearing race 25 preferably being provided. Collar 24 is bolted or otherwise suitably secured to the cross arm 22, as at 26.

Remote control means is provided for either rotating the cross arm 22 at a high speed or for causing it to rotate slowly under the direct operation of the operator. As illustrated, the remote control means includes a transmitting device 2'! and a reproducing device 28, which are similar in construction and are each provided with a poly-circuit armature winding and a single circuit field winding. When the poly-circuit armature winding of each device is physically similar to a three-phased Y or A connected armature winding, transmitting device 21 and reproducing device 28 are connected together by three conductors 29 extending between like points on their respective armature windings. windings are connected together and to a suitable source of alternating current by conductors 30 and 3!.

As is well known to those skilled in the art, the field windings of devices 21 and 28 induce alternating electro-motive forces in their respective armature windings, the relative value of these electro-motive forces depending upon the angular positions between their fields and armature windings. When the rotors of the transmitting device and reproducing device are in an gular agreement, the electro-motive forces induced in the two armature windings are nearly opposite and hence no current is produced in the armature circuit. However, when the rotor of the transmitting device is turned, this voltage balance no longer exists and currents are caused to flow in the armature circuit, and a torque is thereby exerted upon the rotor of the reproducing device. This torque causes the rotor of the reproducing device to rotate until it reaches a position in which the voltages are again balanced, or, in other words, until the rotors of the two devices are again in angular agreement.

It will thus be understood that if the rotor of the transmitting device 2! is moved through an angle of, say, 10 in a clockwise direction, the rotor of the reproducing device 28 will be moved through a similar angle. Furthermore, if the rotor of the transmitting device 2'! is rapidly rotated, the rotor of the reproducing device 28 will be rotated in the same direction at the same speed.

Referring again to Figure 1 of the drawing, manual means for moving the rotor of the transmitting device 27 is shown in the form of a wheel 32 secured to one end of the rotor shaft 33. Power means for driving the rotor .of the transmitting device 27 is shown at 34 as being geared The field to the opposite end of rotor shaft 33 by a su tab e gear drive 35. Power means 34 is connected by means of conductors 36 to a source of electric energy, a switch 31 being provided to open the circuit when deenergization of the power means 34 is desired. From the above description, it is to be understood that the cross bar 22, carrying the reflector H and the director l2, may be rotated at a high speed by closing switch 31; or it may be slowly rotated by opening the switch 3'! and manually turning the manual control wheel 32.

When the short wave radio transmitter 15 is coupled to the antenna array, as shown in Figure 1, a highly directional beam. of radio waves are propagated in a radiation pattern substantially similar to that as shown at A in Figure 2. If the switch 31 of the power supply means 34 is now closed, the cross arm 22 carrying the reflector]! and the director 12 will be rotated at high speed. This has the effect of rotating the radiation pattern A at ,the speed of rotation of the cross arm 22, the resulting effect being much the same as the rotation of a search light at a high speed. If a short wave radio receiving station is located within the range of the transmitter, the beam of radio waves or signal energy will intercept the receiving station once during each revolution of the cross bar 22. This in turn has the effect of causing a series of propagated radio waves to impinge on the radio receiving station intermittently. If the speed of rotation of the radio beam is rapid enough, a persistence of sound effect will be obtained at the receiver which is analogous to the well known phenomenon associated with motion pictures and the like, namely persistence of vision. In other words, if the rate of rotation of the radio beam is rapid enough, an after image of sound effect is obtained which carries over the interval during which no waves are being received by the radio receiver. the radio beam may vary within wide limits without departing from the spirit and scope of the present invention, it has been found in practice that the rate of rotation may be as low as eight to ten revolutions per second, although higher rates of rotation are preferred. It will, of course, be understood by those skilled in the art that the critical speed, above which it is necessary .to rotate the radio beam to obtain an after image of sound eifect, will vary to some extent depending upon the nature of the signal being transmitted. More specifically, it will be understood that the critical speed for effecting an after image of sound effect where there is a modulated carrier wave being transmitted, will be greater than for an unmodulated carrier wave.

The advantage in employing the above type of communication system will be further apparent upon an inspection of Figure 2, wherein the dotted line B indicates the maximum, efiective range for omn-i-directional transmission of radio waves for a given amount of power, while the radiation pattern A shows that the maximum range over which communication may be established is substantially greater for the same amount of power. It will furthermore be apparent that the disadvantage of having to determine the bearing of a radio receiving station has been eliminated without substantially detracting from the effective range obtainable from uni-directional transmission.

A further advantage of my novel method and means for radio communication is illustrated in Figure 2. Assume that a radio receiving station,

While the practical rate of rotation of tuned to the same frequency as transmitter I5, is located on an aeroplane 38 whose bearing from the position T of the transmitter 15 is unknown. The transmitter 15 is energized and is coupled to the antenna it through relay IT and coupling transformer IS. The switch 31 is closed, thus causing the reflector II and director IE to rotate about the antenna It at high speed. The highly directional beam A of radio waves periodically intercepts the aeroplane 38, if it is within the range of the transmitter, and communication is established therewith in the manner described above. Communication having once been established and the operator of the transmitter 15 having been apprised of the fact that the aeroplane is within the range of the transmitter l5, switch 31 is opened to deenergize power supply means 34 and the hand wheel 32 is slowly turned by the operator until communication is again established with the aeroplane 33. This, of course, is assuming that when the switch 31 was opened, the reflector H stopped in such a position that the beam of radio waves no longer impinged on the receiving antenna. After the operator of the receiving apparatus on aeroplane 38 has signaled back that he is again receiving signals from the transmitter 15, the operator of the transmitter ceases to turn the hand wheel 32 and leaves the radio beam at a fixed bearing position. The aeroplane 38 may then follow the beam into the location T of the transmitter, l5.

It will be apparent that my novel method and means of communication not only permits transmission of intelligence over a great distance for a given amount of power, but also provides a homing system for aeroplanes whose bearing and position are originally unknown.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto, since many modifications may be made, and I therefore contemplate in the appended claims to cover all such modifications as fall within the true spirit and scope of my invention.

I claim as my invention:

1. The method of communicating by radio between a first station whose bearing is known and a second station whose bearing is unknown, said method including the step of rotating a highly directional beam of radio waves at a frequency of rotation suificient to produce an after-image of sound in a receiving apparatus located at the second station to establish communication with said station, then transmitting signals from said' second station to said first station, and then slowly rotating said beam while signals are being selectively received at said first station from said second station to determine the bearing oi. the second station.

2. The method of establishing a homing beam for aeroplanes whose bearing and position are originally unknown, said method including the step of rotating a highly directional beam of radio waves at a home station and revolving said beam at a frequency of rotation sufficient to produce persistence of sound in a radio receiver carried by said aeroplane, then trans- Initting signals from said aeroplane to the home station, then slowly rotating said beam while signals are being transmitted from said aeroplane and to determine the bearing of said aeroplane, and then holding the beam at the bearing so determined to provide a beam to guide said aeroplane to said home station.

PAUL H. DAVIS. 

